1. Field of the Invention
This invention relates generally to multi-part seal assemblies and particularly to a multi-part seal assembly adapted for use in sealing the rotatable regenerator of a gas turbine engine.
2. Description of the Prior Art
Special seals have been developed for heavy duty applications such as sealing regenerators in gas turbine engines where the seal is subjected to high pressures and high temperatures. Such seals may have multiple parts loosely joined to allow for thermal expansion and construction. One such seal structure, shown in U.S. Pat. No. 3,761,101 comprises two arcuate portions joined at their ends and a linear crossbar portion extending between the joinder points of the arcuate portions. Each part of the seal includes a relatively thin, flexible base having a high temperature, low friction contact means on one side thereof for sealing engagement with the movable regenerator and a leaf spring mechanism affixed to the other side thereof for making sealing engagement with the engine housing. Where pressure differentials are not extreme, the spring mechanism may simply consist of a single, relatively thin, resilient leaf spring sealing element including a cantilevered portion having a sealing edge for engaging the housing. Where required by greater pressure differentials, the sealing element may be reinforced by a somewhat thicker and stronger leaf spring having a shape which generally conforms to the shape of the sealing element.
Such arrangements work relatively well along the curvilinear portions of the seal assembly which are capable of adjusting to thermal expansion or contraction by varying the angle at which the leaf spring mechanism is cantilevered with respect to the base. However, such compensation is not possible along the linear, crossbar portion of the seal assembly. It has been observed that the differences in the expansions (and contractions) of the sealing element on the one hand, and the base and reinforcing leaf spring member on the other eventually result in permanent deformation, in the form of rippling, of the sealing element thereby destroying the integrity of the seal. The sealing element must thus be replaced after each period of operation and renders the engine unsuitable for applications, such as in the automotive field, where the engine is subject to intermittent starting and stopping.